Picosecond and nanosecond nonlinear transmission measurements were used to determine the excited singlet and triplet state absorption cross sections at 532 nm for group IVA metalloid phthalocyanines. A five-state rate-equation model is used to analyze the nonlinear transmission data. The successful simulations of the nonlinear transmission data on this series of phthalocyanines for widely differing pulse durations provide strong evidence for the validity of the excited state absorption model. Use of the heavy atom effect has allowed engineering of phthalocyanines with strongly enhanced optical limiting performance.